Affected individuals attempt to release nervous energy by cracking their joints, most often their knuckles. If the cracking is suppressed, they experience tension and an urge to perform the behavior.
Joint cracking is a common habit. Knuckle cracking – the most common form – is seen in approximately 25 (Castellanos & Axelrod, 1990) to 45 percent (Swezey & Swezey, 1975) of the population (Boutin et al., 2017).
Over-stretching the knuckles to the point of causing a cracking sound can cause swelling and joint weakness.
Habitual knuckle cracking can lead to decreased strength of grip and, in some cases, even functional impairment of the hand. In contrast, cracking of the neck can lead to serious damage (z.B. Deǧtrmenci et al., 2011).
Trichophagia (“hair eating”, the eating of pulled-out hair – or sometimes just licking one’s hair), refers to the repeated swallowing of hair and is classified as an additional symptom of trichotillomania.
Prevalence in individuals with trichotillomania
About 5 to 20 percent of individuals with trichotillomania also suffer from trichophagia. This behavior appears to be more common in individuals under the age of 30 (Christenson, 1991; Grant & Odlaug, 2008).
The swallowed hair—also known as a hair bezoar—can clump together in the stomach or intestines and may cause serious medical complications.
People who are affected by dermatophagia (“skin eating”) repeatedly bite their own skin, leaving it bloody and damaged. The disorder is referred to by some experts as a subtype of skin picking or nail biting (para-onychophagia).
Affected individuals typically bite the skin surrounding their fingernails and knuckles.
If the behavior persists over a longer period of time, calluses may form in these areas, which may increase the urge to bite the affected areas.
Boutin, R. D., Netto, A. P., Nakamura, D., Bateni, C., Szabo, R. M., Cronan, M., Foster, B., Barfield, W. R., Seibert, J. A., & Chaudhari, A. J. (2017). “Knuckle cracking”: can blinded observers detect changes with physical examination and sonography? Clinical Orthopaedics and Related Research, 475(4), 1265–1271. https://doi.org/10.1007/s11999-016-5215-3.
Castellanos, J., & Axelrod, D. (1990). Effect of habitual knuckle cracking on hand function. Annals of the Rheumatic Diseases, 49(5), 308–309. https://doi.org/10.1136/ard.49.5.308
Christenson, G. A., Mackenzie, T. B., & Mitchell, J. E. (1991). Characteristics of 60 adult chronic hair pullers. The American Journal of Psychiatry, 148(3), 365–370. https://doi.org/10.1176/ajp.148.3.365
Deǧtrmenci, E., I̊pek, M., Kiroǧlu, Y., & Oǧuzhanoǧlu, A. (2011). Wallenberg Syndrome following neck cracking: a case report. European Journal of Physical and Rehabilitation Medicine, 48(1), 167–168. https://europepmc.org/article/med/21508912
Grant, J. E., & Odlaug, B. L. (2008). Clinical characteristics of trichotillomania with trichophagia. Comprehensive Psychiatry, 49(6), 579–584. https://doi.org/10.1016/j.comppsych.2008.05.002
Swezey, R. L., & Swezey, S. E. (1975). The consequences of habitual knuckle cracking. The Western Journal of Medicine, 122(5), 377–379.